The present invention relates to polyphenylene sulfide (hereafter, sometimes referred to as "PPS") resin composition for producing molded articles which composition can be molded into articles with causing less corrosion to the metallic mold used upon their fabrication or molding of to metal portions used in various built-up parts comprised by such molded articles.
As is well known, PPS resins generally have very high heat resistance, chemical resistance, electric properties and fire resistance, and they exhibit excellent mechanical strength, rigidity and dimension stability by blending them with a reinforcing filler or the like, resulting in that they are used widely for molding various articles such as electric and electronic parts, parts of cars and those of machines.
However, the conventional PPS resins generate gas or gases corrosive to metals at high temperatures or under molten conditions, which causes various problems that metallic molds and molding machines could be corroded upon molding or that upon aging molded articles at temperatures not lower than 100.degree. C. and not higher than the melting point, corrosion could occur to metal portion of built-up parts comprised by the molded articles or to insert metal parts.
For example, when PPS resins are used as a relay base, the metal contact of the relay would be corroded to cause contact failure, or to deteriorate adhesion strength of solder at the insert metal portion would decrease due to corrosion.
More particularly, there are now observed two types of problems currently recognized as being involved in the corrosion of metals due to PPS resins corrosions may roughly be grouped into two types. One is the occurrence of the corrosion of metallic mold or the like upon melting PPS resin, and the other is that the corrosion of silver plated terminals or the like upon aging at temperatures lower than the melting point of the resin.
There have heretofore been known a method in which alkali metal hydroxides or carbonates are added as described in U.S. Pat. No. 4,017,450 and a method in which hydroxides, oxides, aromatic carboxylate of metals belonging to the Group IIA of the periodic table are added as described in Japanese Patent Publication (Kokai) No. 62-109850.
However, in both cases, no satisfactory effect can be obtained. Particularly, it can be said that no effect is obtained on the prevention of the occurrence of silver corrosion, for example, when PPS resin is aged at temperatures not lower than 100.degree. C. and not higher than the melting point of the resin. Furthermore, since the additive itself is water-soluble or hygroscopic, if not water-soluble, the addition of additives as described above leads to decrease in the water resistance of the resulting composition and therefore, when PPS resin is used, for example, as an insulating material reinforced with glass fiber, this causes decrease in the insulating property of the material to a greater extent at high humidity.
Also is known a method in which hydrotalcite is added to PPS resin in order to reduce the corrosion of metals as described in U.S. Pat. No. 4,529,769. This method, however, is inferior to the preceding proposals in which the alkali metal hydroxides or carbonates are added in the primarily expected effect of reducing the corrosion of metals which would occur to metallic molds although less decrease in the insulating property of the composition is attained by the method.
There are known a composition for molding electronic parts which comprises PPS resin and zinc oxide and a method for preventing the color shift thereof as described in Japanese Patent Publication (Kokai) No. 59-181408. The zinc oxide-added PPS composition still has disadvantages not only that insufficient effects can be obtained for preventing the corrosion of metallic molds upon melting PPS and that of silver-plated terminals and the like upon aging at a temperature not higher than the melting point of PPS but also that the addition of such compound even in small amounts decreases greatly the strength of the resulting composition.